The call completion ratio is an important index to measure the network performance and directly influences the call experience of users. If the call completion ratio is low, a user will initiate a call request again if the user has one dial-up failed, which not only decreases the user experience, but also wastes network resources, and simultaneously, causes easily problems such as network congestion, etc. Therefore, how to improve the service call completion ratio has become an important research subject.
FIG. 1 is a flow chart of a successful service establishment in the related art. As shown in FIG. 1, when a User Equipment (UE) initiates one call according to 3GPP technical specifications, firstly the UE sends a Radio Resource Control (RRC) connection request to a Radio Network Controller (RNC); the RNC allocates radio resources for the UE and sends a RRC connection establishment message to the UE to guide the UE to establish a signaling radio bearer; and the UE sends a RRC connection establishment completion message to the RNC after completing the RRC radio resource configuration. After the RRC signaling connection establishment process is completed, the UE performs Non Access Stratum (NAS) signaling interactions with a Core Network (CN) through direct transfer messages; the CN sends a service assignment message to the RNC; the RNC receives the assignment message, allocates a service bearer for the UE and sends a radio bearer establishment message to the UE to guide the UE to establish a service radio bearer; and the UE sends a radio bearer establishment completion message to the RNC after completing the configuration. The RNC returns a service establishment completion message to the CN after receiving the radio bearer establishment completion message.
The call failure may be caused by many factors, among which the call failure resulted from the quality of the radio environment is particularly prominent. During the call establishment process, the RNC sends the radio bearer establishment message to the UE and waits the UE to return a response. FIG. 2 is a flow chart of air interface failures in the related art, and as shown in FIG. 2, the quality of the air interface causes several failures as follows: I. the UE is unable to correctly receive a Radio Bearer (RB) establishment message from the network side (210); II. the UE receives the RB establishment message and returns a response, but the network side does not receive the response (220); III. the UE receives the RB establishment message, but a radio link failure is detected during the reconfiguration process, and therefore the reconfiguration flow ends (230). The above situations finally cause the service establishment failure (240).
When the quality of the air interface deteriorates, the UE will detect the radio link failure of the physical layer or the unrecoverable error of the Radio Link Control (RLC) layer, notify the RRC layer, and initiate a cell update message with a cause of “Radio Link Failure” or “Unrecoverable RLC”. After receiving the message, the RNC executes the reestablishment flow of the radio link wherein firstly the RNC deletes the radio link corresponding to the UE, and switches into the public status; and then the RNC prepares establishing a new link, and sends a cell update acknowledgment message in a downlink public transmission channel in order to send the new configuration information to the UE. To make the description simple and convenient, this process is called call reestablishment in the present invention.
Although the call reestablishment may solve the problem of the deterioration of the quality of the air interface, there are still two problems in the case of call failures:
(1) Although call reestablishment may retrieve calls through the reestablishment of the radio link, it is necessary to ensure that configurations at both the network side and the UE side must be kept synchronous, and due to the complexity of the quality of the air interface, the RNC is unable to accurately determine the current status of the UE.
(2) During the service establishment process, if the quality of the air interface deteriorates and the UE reports the cell update, the RNC may retrieve calls by executing the call reestablishment flow. However, if the UE does not report the cell update in time, the call drop will be caused, and thereby the service call completion ratio is greatly reduced.